1. Field of the Invention
The invention is generally related to methods of laser and/or photon transfer.
2. Description of the Prior Art
Direct write technologies have gained popularity with the increased interest in biological sensors and microarrays, and the push for engineered tissues to replace organ transplants. These techniques allow for increased ability to manipulate biological materials in very small volumes with much better accuracy than has been previously possible. Some of the most promising techniques for use in controlling and transferring biological materials are matrix assisted pulsed laser evaporation direct write (MAPLE DW, see U.S. Pat. No. 6,177,151 to Chrisey et al. (all referenced patents, patent applications and publications are incorporated herein by reference), dip-pen nanolithography (DPN), scanning probe microscopy (SPM), microcontact printing (MCP), and laser guidance direct write.
MAPLE DW focuses a pulsed laser source at the interface of a quartz “ribbon” (analogous to a typewriter, it is usually a quartz slide with a coating containing a mixture of a matrix support material and the biological materials of interest) to cause the ablation of a small amount of the interfacial matrix material, which then causes the remaining bulk matrix and biological material to be expelled from the ribbon in a bubble-jetting effect. The expelled material travels through-space, away from the laser and ribbon to a receiving substrate. This results in a spot of transferred material approximately 100 μm in diameter with pL scale volumes. MAPLE DW has limited applications or inherent limitations due to the physical properties of the biological materials and surrounding media needed to ensure accurate pattern formation. Specifically, MAPLE DW requires that a mixture of transfer material and a matrix material be presented to the laser source. The matrix must be of higher volatility than the transfer material and strongly absorb the incident radiation. In addition, the reproducibility of the technique can be low due to inconsistencies in the parameters necessary for ablation of the matrix material. Also, because the absorptivity of certain matrix materials is quite low, there is the potential for damage to biological materials from direct and indirect interaction with the incident laser radiation.
DPN and SPM are direct-write techniques that offer the possibility of writing very small amounts of material. DPN has been used to write lines of collagen 30-50 nm in width. Both these techniques have been used to lay down patterns of organic adhesion molecules, which are then used for adhesion of biological molecules of interest. This leads to difficulty in patterning multiple biological material types and difficulty in rapid design of micro-scale constructs.
MCP techniques utilize biomaterial coated polymer stamps to transfer biomaterials to more adhesive substrates. It is possible to obtain sub-micron features using MCP, but there is little control over the amount of material transferred. It is possible that different materials could be patterned using multiple stampings, but this could lead to possible contamination of stamps and has inherent limitations in the proximity of the different material types. Also, MCP is dependent on biomaterial-substrate adhesion, and therefore not universal to all substrate materials.
Laser-guided DW uses a “loose” form of optical trapping to guide cells along the beam axis and to a receiving substrate. The use of a low NA lens allows for a continuous stream of cells or molecules to be transferred to a target substrate. This technique allows for manipulation and placement of individual cells, but has limitations in the fact that it can take hours to write a moderate number of cells. In addition there is the potential for DNA damage from the extended time that cells or other biological materials are exposed to the laser beam.
Laser transfer of biological materials presents a challenge due to the fragility of many biological materials. They can be harmed by shear stress when they are removed from the target substrate and by impact stress when they land on the receiving substrate. DNA in particular can be uncoiled by such stresses. Heat can denature many biological materials. UV damage can also result when a UV laser is used.
In some other techniques, the target substrate is coated with several layers of materials. The outermost layer, that is, the layer closest to the receiving substrate, consists of the material to be deposited and the innermost layer consists of a material that absorbs laser energy and becomes vaporized, causing the outermost layer to be propelled against the receiving substrate. Variations of this technique are described in, for example, the following U.S. patents and publications incorporated herein by reference: U.S. Pat. No. 5,308,737 to Bills et al., U.S. Pat. No. 5,171,650 to Ellis et al., U.S. Pat. No. 5,256,506 to Ellis et al., U.S. Pat. No. 4,987,006 to Williams et al., U.S. Pat. No. 5,156,938 to Foley et al. and Tolbert et al., “Laser Ablation Transfer Imaging Using Picosecond Optical pulses: Ultra-High Speed, Lower Threshold and High Resolution” Journal of Imaging Science and Technology, Vol. 37, No. 5, September/October 1993 pp. 485-489. A disadvantage of these methods is that they can still expose the material to be deposited to high amounts of energy that may not be suitable for biological materials.